Valid Sudoku

最后一个循环的问题比较值得学习，本质是n皇后

public class Solution {
    public boolean isValidSudoku(char[][] board) {
        //http://blog.csdn.net/linhuanmars/article/details/20748171
        if(board==null || board.length==0) return false;
     
        for(int i=0; i<9; i++){
            boolean [] row = new boolean[9];
            for(int j=0; j<9; j++){
                if(board[i][j]!='.'){
                    if(row[(int) (board[i][j]-'1')])
                        return false;
                    row[(int) (board[i][j]-'1')]  = true;
                }
            }
        }
        
        for(int j=0; j<9; j++){
            boolean[] col = new boolean[9];
            for(int i=0; i<9; i++){
                if(board[i][j]!='.'){
                    if(col[(int) (board[i][j]-'1')])
                        return false;
                    col[(int) (board[i][j]-'1')]  = true;
                }
            }
        }
        
        for(int b = 0; b<9; b++){
            boolean[] blk = new boolean[9];
             for(int i=b/3*3; i<b/3*3+3; i++){
                 for(int j=b%3*3; j<b%3*3+3; j++){
                    if(board[i][j]!='.'){
                        if(blk[(int) (board[i][j]-'1')])
                             return false;
                        blk[(int) (board[i][j]-'1')]  = true;
                    }
                 }
             }
        }
        return true;
    } 
}